Photovoltaic devices are capable of converting solar radiation into usable electrical energy. The energy conversion occurs as a result of what is well-known in the solar cell field as the photovoltaic effect. Solar radiation impinging on a solar cell and absorbed by a semiconductor body, such as hydrogenated amorphous silicon, generates electrons and holes. The electrons and holes are separated by a built-in electric field, for example, by a rectifying junction such as a Schottky barrier, in the solar cell. The electrons generated at the interface of the Schottky barrier material and an N-type semiconductor body flow toward the semiconductor body where said electrons are collected. The separation of electrons and holes results in the generation of an electrical current known as the photocurrent.
The photovoltage or open circuit voltage of the solar cell is dependent, inter alia, upon the height of the barrier between the semiconductor body and the Schottky barrier material. C. R. Wronski et al, Solid State Communications 23, 421 (1977), have reported barrier heights of up to about 1.1 eV with high work function metals such as platinum contacting intrinsic hydrogenated amorphous silicon. Although the energy gap of hydrogenated amorphous silicon varies with the concentration of hydrogen up to the bandgap energy of about 1.7 eV, the value of the open circuit voltage of the solar cell is dependent upon the barrier height of the Schottky barrier material. Thus, to maximize the open circuit voltage of a solar cell, it would be highly desirable to have a material wherein the barrier height between the material and the semiconductor body is approximately as large as the bandgap energy of the semiconductor.